Cyclization of hydrocarbons



' been studied in considerable detail.

Patented Apr. 27, 1943 UNITED STATES PATENT OFFICE CYCLIZATION OFHYDBOCARBONS Bernard 8. Greensielder, Berkeley, Calif assignor to ShellDevelopment Company. San

Francisco, Call! a corporation of Delaware No Drawing. ApplicationFebruary 27, 1941,

Serial No. 880,893

16 Claims. (01.269-668) hydrocarbons is, however, as by-products fromthe distillation of coal. Consequently; their supply is primarilydependent upon the condition of the steel and coal tar industries and isin any case limited. Aside from the myriad of uses where theirapplication is. more or less obligatory, aromatic hydrocarbons have agreat many potential uses which have been hitherto curtailed by thelimited supply and relatively high prices. For example, aromatichydrocarbons of. relatively low molecular weight have become ofincreasing importance for use as solvents, etc. and especially ascomponents of liquid fuels in view of their excellent ignitioncharacteristics. view'of these circumstances there is an urgent demandfor a practical and economical process whereby aromatic hydrocarbons maybe produced from other sources.

The most promising source of aromatic hydrocarbons, other than coal tar,is petroleum.

Aromatic hydrocarbons can be produced from petroleum hydrocarbons, atleast theoretically, in any one of several ways, all of which have It isknown. for example, that aromatic hydrocarbons are produced fromnon-aromatic petroleum hydrocarbons under severe thermal crackingconditions. Thus, cracked distillates obtained from high temperature 1'more or less severe cracking operations genera y contain a certainamount of aromatic hydrocarbons. This method is, however, generallyimpractical for the production of may be produced by the thermaltreatment of light hydrocarbon gases at high temperatures according tothe Fischer process. This process,

however, requires temperatures in the neighborhood of 1000 C. to 1300 C.and requires the use oi. a large number of expensive alloy reactiontubes of extremely small dimensions. The process furthermore tends togive relatively low yields oi! aromatic hydrocarbons which arepredominantly of the less desired polynuclear type.

It has been found that aromatic hydrocarbonsv may be synthesized by thecatalytlccyclizationdehydrogenation oi open chain hydrocarbons. This newreaction holds considerable promise in that it allows aromatichydrocarbons to be pro-. duced in almost any desired quantities frominexpensive and readily available hydrocarbons and particularly thenormal aliphatichydrocarbons which, in view of their poorignitioncharacteristics, areleast desirable for gasoline-type fuels.- Afurther advantage which can-be gained bythe utilization ofcatalytic'cyclization is that, it naphth'enic hydrocarbons are "presentin the hydrocarbon" fraction treated, these may be simultaneouslydehydrog'enated to aromatic hydrocarbons, thus increasing the yield. Inview of'the great possibilities aflorded by the cyclizapure aromatichydrocarbons or highly aromatic hydrocarbon fractions in view oi the lowyields, excessive production of gas and extensive treatment required toseparate the aromatic hydrocarbons formed ,from olefines, diolefines Iand other crackedproducts which are simultaneously formed.

It is also known that aromatic hydrocarbons tion reaction, a great dealof'workhas been done to bring this reaction into the realm of practicalapplication. f 1 Y The production-5 1' aromatic hydrocarbons bycyclization' requires catalysts having'dehydrogenating activity. Thishas been considered by some to indicate that the conversion 01' openchain hydrocarbons to aromatic hydrocarbons is a multi-step reaction"involving dehydrogenation. It is therefore sometimes referred to as*cyclizanon-dehydrogenation." "dehydrogenation-cyclization" anddehydrocyclization." It is known, howeventhat the cyclization ability ofa given catalyst involves more than simply its dehydrogenating ability.Although nearly all classes of dehydrogenating catalysts have beeninvestigated with regard to their possible. cyclization activities, onlya relatively few. have been iound'to exert an appreciable cyclizationactivity. Cyclization activity appears .to be practically confined tocompounds of metals of the left-hand columns of groups IV, V and VI ofthe periodic table.

Of these, those of group VI and especially chromium are by far the mostactive.

The cycliza-tion ability of the various. cata-' lytic metal compoundsis, in general, relatively little aflected by the type of compound inwhich the metal-is combined. Thus, for example, the

oxides, sulfides, halides, selenides, tellurides,

phosphates, manganates, molybdates, chromates, chromites, tungstates,etc. or mixtures thereof may generally be employed. Generally speaking,

erably used in the form of their oxides.

These cyclizing metal compounds per se are, however, not generallysuited for practical application due to. the fact that they quickly losetheir cyclizing activity in use. In order to produce aromatichydrocarbons in a more econom I alumina gels, activated bauxite and thelike. A

particularly effective adsorptive alumina is that prepared according tothe process of U. S. Patent 1,868,869 and commonly used'in the tradeunder the name "activated alumina.

The cyclizing metal compound and relatively inactive stabilizingcompound may be employed in a wide range of proportions. In general,however, the stabilizing material functions also as a carrier materialand is used in excess. Suitable catalysts may comprise, for example, anadsorptive and stabilizing carrier material supporting from 2% to 30% ofa catalytically active metal in the form of a suitable compound such asan oxide, sulfide, or the like.

- These supported catalysts may be prepared in any one of severalconventional manners. A convenient method comprises impregnating asuitable carrier in the form of granules or pellets of the desired sizewith a solution of a compound of the metal which it is desired tocombine with the carrier, and then drying. The concentration of theimpregnating solution used in this particular case will depend upon thesolubility of the particular metal compound at the temperature of theimpregnation and upon the desired concentration of the metal compound inthe compound catalyst. 'I he procedure followed in drying or treatingthe impregnating material will vary depending upon the chemicalconstitution of the compound catalyst. In general, the material can bedried in air at temperatures as high as 800 C. or even higher in somecases. In other cases, it may be desirable to effect the drying withinert gases such as nitrogen, or reducing gases such as hydrogen,hydrocarbons,

etc.

active cyclizing constituentsof the combined catpregnation of thecarrier "with their aqueous solutions. In such cases, the stabilizingcarrier Many of the compounds hioh are desired as however, the variouscyclizing metals are prefwhich can be converted to the desired metaloxide, metal sulfide or the like by calcination,

hydrogen sulfide treatment, or the like, of the impregnated material. Acyclizing metal oxidecontaining catalyst may also be obtained byprecipitating a corresponding metal hydroxide on the surface of thecarrier and subjecting the thus-obtained material to calcination undersuitable temperature conditions.

The catalysts prepared as described are often submitted to apretreatment rior to their use. Thus, for example, they are often heatedfor some hours at temperatures between about 300 C. and 600 C. in thepresence of reducing gases such as hydrogen, hydrogen sulfide, hydrogenplus natural gas, etc. Such pretreatment usually improves their activitysomewhat.

The process of cyclization-dehydrogenation to produce aromatichydrocarbons using cyclizing metal compound catalysts is especiallysuitable for the production of aromatic hydrocarbons and relativelysimple mixtures of aromatic hydrocarbons from individual hydrocarbonshaving prefmay be impregnated with a solution of a salt erably not morethan twelve carbon atoms in an open chain and capable of being cyclizedto sixmembered rings and/or hydrocarbon mixtures containing one or moreof such hydrocarbons in appreciable quantities. Thus, it is applicableto the economic production of mono-nuclear aromatic hydrocarbons fromhydrocarbons containing at least six and preferably not more than twelvecarbon atoms in an open chain. For example, the predominant aromatichydrocarbons i'ound in the product when treating a few of such openchain hydrocarbons are shown in the following table:

' Table I Open chain hydrocarbon Predominant aromatic hydroemployedcarbons found in the reaction product N B N T A -methyl hexane Do.

Ortho xylene. Para xylene. Ortho methyl ethyl benzene. Ortho methylpropyl benzene.

Benzene.

Do. Orthoxylene.

The process is also applicable for the production of poly-nuclearhydrocarbons from aikylated cyclic hydrocarbons, such as n-butylbenzene, n-amyl benzene, n-butyl eyclohexane, crotyl benzene, and thelike. Of the various appllcable hydrocarbons, so that better resultsare, in general, obtained with normal and slightly branchedhydrocarbons. Applicable hydrocarbon mixtures may also contain higherand/or lower boiling cyclizable and non-cyclizable hydrocarbons such asnaphthenic hydrocarbons, paraflinic hydrocarbons, oleflnic hydrocarbons,and the like. Thus, for example, normal heptane may be cyclized in thepresence of methane, ethane, ethylene, benzene, toluene, octane, 2-methyl pentane, and the like, and excellent yields of toluene obtained.I have found, however, that materially improved catalyst life andtherefore operating economy can be realized when treating hydrocarbonmixtures containing lower boiling non-aromatizable hydrocarbons, if suchmixtures are first treated to remove the easily dehydrogenated andnon-aromatizable butanes and pentanes. Isopentane, when present insubstantial concentrations in the hydrocarbon aamoes of parafllnic andoleflnic hydrocarbons in light petroleum fractions, such as gasoline,etc.. into aromatic hydrocarbons. By treating such petroleum fractions,their aromatic content is considerably increased (any hydro-aromatichydro-. carbons which may be present are also dehydrogenated to aromatichydrocarbons), very little cracking occurs and a stable product of lowoleflne content and increased anti-knock properties is obtained. Thehydrocarbon treated is preferably substantially free of water and/orcompounds, such as the alcohols which form water under the reactionconditions.

The hydrocarbon or hydrocarbon mixture to be treated is preferablypassed as a vapor through a bed of th catalyst supported in a suitableconverter and maintained at the desired temperature by any suitableheating means. While pressures both below and above atmospheric pressure(for instance, 0.01 to 50 atm.) are applicable, the process is usuallyexecuted in practice at atmospheric pressures or thereabouts, forinstance, 1 to 10 atm. r

In order to' produce the best yields of aromatic hydrocarbons andrealize the maximum efllciency of the catalyst, the cyclization isusually effected at a temperature between about 350 C. and 700 C.Temperatures lower .than about 400 C. are, in general, less desirablesince they require low space velocities and give low conversions.Temperatures above about 600 C. allow much higher space velocities andhigh conversions but are, in general, less desirable since they usuallylead to cracking and carbon deposition.

The contact time required to effect the formation of aromatichydrocarbons by catalytic cyclization-dehydrogenation of open chainhydrocarbons is usually considerably longer than that required fordehydrogenation and usually is'at least five seconds. Suitable contacttimes for operation in the above temperature range are, for instance,between about six seconds and two minutes. When operating within apreferred temperature range of about 450 C. to 550 C.,

optimum results are usually obtained with contact times between aboutsix-and eighty seconds. The catalytic reaction is often executed in thepresence of added hydrogen. The ratio of hydrogen to hydrocarbon mayrange, for example;

from up to about 5 mols per mol. The presence of hydrogen, it is found,tends to prolong the life of the catalyst by inhibiting side reactionswhich lead to tar and carbon formation. The use of added hydrogen isconsequently of most advantage when treating complex hydrocarbonmixtures such as cracked gasoline stocks, etc..

which ordinarily tend to tarand coke up the catalyst relatively quickly.The cyclizaton reaction is, however, inhibited by excessive hydrogenpressures. When hydrogen is used, its partial pressure is thereforepreferably kept below- The object of the present invention is toprovide' a method whereby aromatic hydrocarbons may be produced fromopen chain hydrocarbons through catalytic cyclization-dehydrogenation ina more advantageous manner, more particularly by providing a methodwhich is particularly designed to take advantage of short cycleoperation and which gives increased conversions. Specific objects of theinvention are to' provide an improved method for the production ofaromatic hydrocarbons from single open chain hydrocarbons and simplemixtures thereof and to provide a more efllcient method for theimprovement of gasoline stocks, blending stocks and other hydrocarbonfractions through the catalytic conversion of relatively less desirableopen chain hydrocarbons therein to valuable aromatic hydrocarbons.

Through a lengthy investigation of catalysts with respect to theircyclization activity, it has been found that the above-described methodfor the catalytic cyclization of open chain hydrocarbons to aromatichydrocarbons may be considerably improved by employing, in lieu of theconventional catalysts, catalysts which are specifically promoted forthe cyclization reaction by the incorporation therein of relativelysmall amounts of certain promoter metals. It has been found that whencertain small amounts of platinum and/or palladium are incorporated inthese conventionaicyclization catalysts, as hereinafter more fullydescribed, their cyclization activity is markedly promoted and that whensuch pro-.

moted catalysts are employed in otherwise'conventional cyclizationprocesses, greatly improved yields may be obtained. The more or lessspecific promoting effect ofplatinum and palladium on the cyclizationactivity of these catalysts is contrary to expectations since thesemetals per'se are relatively poor cyclization catalysts. I -It has beenshown, for'instance [J. Gen. Chem. (U. S.

S. R.) 9, 496 (1939)] that with a platinum cata lyst the conversions ofparafiln hydrocarbons to aromatic hydrocarbons are only in the range of1% to 6%. Furthermore, the amounts of platinum and/or palladium requiredas promoters are quite small. and far less than needed for even a poorcyclization. Furthermore, this promoting. effect is practicallyconfined-to these metals.

Other metals of group VIII of the periodic sys-' tem are not equivalent.Ofithe materials which have beenfound to act as specific-promoters forcyclization, namely. platinum and/or palladium,

platinum is preferred. v p

The .quantity of promoter metal or mixtureof promotermetals'incorporatedin the cyclization catalyst in order to exhibit thedesired promoter 7 promoting a cyclization catalyst with platinum," forinstance, it may be impregnated, with asuitable solution of] platinumchloride. Other soluble salts of platinum and/or palladium may also I beemployed. Thus, for example, in the case of platinum one mayimpregnate'the cyclization catalyst with'fsuitable solutions of saltssuch as ammonium platinum chloride, alkali platinum chloride,-bariumplatinum cyanide, etc. The impregnate'd solutions may be prepared witheither water or alcohol, or mixtures thereof. In impregnating thecyclization catalyst with such solutions of promoter salts, it ispreferable to employ solutions of such concentrations that theentireimp'regnating solution is taken up by the catalyst. Inthis waycatalysts having uniform and predetermined compositions may be mosteasily prepared without loss of valuable promoter salts, displacement,or the like.

. The catalyst impregnated with the solution of the promoter substancemay be treated in the manners conventional in making platinum orpalladiumcatalysts to convert the impregnated promoter compound to themetal. Thus, for example, the impregnated catalyst may be dried at 5(RC.-150 C. and finally heated to, for instance, 450%. The catalyst maythen, if desired, be pretreated with a reducing gas as described above.

The platinum and/or palladium promoters employed in these catalysts, itis found, act altocargoes is applied to a cyclizing metal compoundsupported upon an alumina carrier than when it is gether differentlythan when employed as catalysts per se. For instance, it is known thatplatinum and palladium are notoriously susceptible to poisoning bysulfur and similar catalyst poisons. When employed as promoters forcyclizing metal compounds in the cyclization of open chain hydrocarbons,however, it is found that such catalyst poisons have no apparent adverseeffect. Thus, for example, a catalyst promoted by platinum can be usedin the cyclization of open chain hydrocarbons with sulfur as mercaptanor hydrogen sulfide actually added to the feed without impairing thecyclizing activity. It is found, however, that the activity of thecyclizing catalysts is adversely affected by sulfates in the catalystmass. When promoting cyclizing catalysts with platinum or palladium,therefore, it is preferable that soluble sulfates, if these are presentin appreciable concentrations, be first removed. Also, the' impregnatingsolutions are preferably substantially sulfate-free. Thus, for example,when impregnating a suitable carrier with chromium oxide, superiorresults may be obtained by employing chromic acid or chromium nitratewhich has been purified to remove sulfate impurities. Alkali metalcompounds (except the sulfates), on the otherhand, are not usuallydetrimental. In fact, it is found that small amounts of potassium orpotassium compounds (other than the sulfate) are beneficial and thatcatalysts containing potassium (preferably 5% to 15% of the amount ofmetal in the cyclizing metal compound) along with the platinum and/orpalladium are somewhat superior. Sodium, when present in appreciableconcentrations, is known to exert a poisoning action on cyclizingcatalysts. In small amounts, however, its presence may be ignored.

While the property of platinum and palladium to selectively promotecyclization appears to be general to all cyclizing metal compounds it isnot equivalent in all catalysts. It appears to depend somewhat both uponthe specific cyclizing metal compound promoted and upon the carriermaterial employed. In general, the promoter effect is most pronouncedwith metal compounds having the strongest cyclizing activity. Thus, theplatinum and/or palladium promoters may be most advantageously employedwith a supported chromium oxide catalyst. The reason for the differencein promoting action caused by the carrier material is not understood. Itis, however, very clearly evident. It is found that the promoter effectis more pronounced when the promoter type.

supported upon other conventional carriers. Fur- 'thermore, all aluminacarriers are not equivalent.

It is found that the promoting effect of platinum and/or palladium ismuch more pronounced when the alumina carrier material consistsessentially of or contains appreciable quantities of aluminaalpha-monohydrate. Such a material is Activated Alumina. ActivatedAlumina" is a particular form or kind of alumina prepared from the scalydeposits formed in the Fickes- Sherwin modification of the Bayerprocess, according to the process described in U. 8. Patent 1,868,869.

The cyclization-dehydrogenation of open chain hydrocarbons usingcatalysts promoted with platinum and/or palladium, according to theprocess of the present invention, is illustrated in thefollowing'examples. These examples, which are in'the nature of selectedcarefully executed comparable experiments carried out under favorableconditions with a few typical catalysts and with a simple representativehydrocarbon rather than illustrations of suitable applications of theprocess with a wide variety of catalysts and hydrocarbon stocks, werechosen for the purpose of illustrating and emphasizing various aspectsof the promoting effect discussed above and should not be consideredaslimiting the invention in any way. I

Example I Excellent cyclization catalysts of the conventional typehaving the following compositions Or (as chromium 23:? Support Per cent"Activated alumina do -.-.do

were employed under the following nearly optimum conditionsTemperature=490 C. Pressure=1 atmosphere Liquid hourly spacevelocity==0.33

for the cyclization-dehydrogenation of pure normal heptane to toluene.The conversions to toluene obtained initially, at the maximum, and afterfive hours of operation are given in the following table:

Conversions Time Catalyst Catalyst Catalyst 183 184 185 Per cent Percent Per cent Initial Maximum conversion Five hours Example II p Aquantity of catalyst having the same composition as catalyst 184described above was impregnated with 0.17% platinum (catalyst 176). as0.087% platinum about doubled the conver- This platinum-promotedcatalyst was appliedfor sions to toluene obtained in a process period ofthe cyclization-dehydrogenation of normal hepten hours. It is also seenthat, although the contane under the same conditions as those 'ofExversions obtained in both'cases with the proample I. The conversionsto toluene obtained 5 moted catalyst were much higher than those obwereas follows (the results obtained with catalyst tained with theunpromoted catalyst, the bromine 184 are included for comparison):numbers of the products were lower. This is unexpected and is due to thefact that the platinum Conversions promoter is quite specificand isprimarily efiec- Time tive in increasing the cyclization activity of theCatalyst Catalyst catalyst- 170 184 Example V Perm! pm Severalcomparable chromium oxide-alumina eggg: y :3 cyclization catalysts wereprepared and some Five hours 50 41 were promoted for cyclization withsmall amounts of platinum. Their active component From this example itis seen that by promoting P were as a conventionalcyclization-dehydrogenation catalyst with a small amount of platinum,much Chromium better yields of aromatics may be obtained. Catamm oxidePlath Example I]! 0 An excellent cyclization-dehydrogenation cat-. 3,;8%: 8- zn 8 96 alyst (No. 57) of the conventional type prepared fig0.39? 0.0427 Pt. by impre n n n adsorptive alumina w :4"C;:: 3233,zfiiiii 312 9 71915.

10.5% chromium (as chromium oxide) wasused in thecyclization-dehydrogenation of pure normal heptane under the followingnearly optimum conditions:

Temperature=490 C.--

Pressure=10 atmospheres Diluent=Hydrogen, 1 moi/3 mois heptane .Contacttime=70 seconds These catalysts were used for thecyclizationdehydrogenation of normalheptane under the followingconditions:

Temperature=490 C. Pressure=l atmosphere Liquid hourly spacevelocity=0.33

The initial conversions, maximum conversions, The following results w pand average conversions over the first 7 10,

Average conversion to toluene and 25 hours are given in the followingtable:

over the first ten hours=7% Bromine number of the product=11 M 40Initial axi- Average conversion over When the "hydrogen diluent wasreplaced with Catalyst No. OOnVetmum nitrogen in a comparableexperiment, the folsion 7 hrs, 1 mm 25 hm lowing results were obtained:

Average conversion to toluene Pericmt Per cent Per cent -41 7 a1 overthe first ten hours=12% 230.6 46.9 33.4

Bromine number'of the product=14 5 3 2 These experiments illustrate theresults obtain- 2; g

able under favorable conditions with one of the best prior artcyclization catalysts for medium time cycle operation. The distinctretardation of the cyclization reaction caused by the 2% atmospherespartialpressure of hydrogen is readily apparent.

From these results it is seen that, although concentrations of platinumpromoter as small as 0.3 of the chromium concentration in the catalyst(catalyst 233) are efiective in materially increasing the initialconversion, such amounts do Example IV not produce the optimum promotioneven for fairly sh rt ycle peration (compare for eximilar to theabove-described catg gg zgg i 133% chromium as ample, the averageconversions over the first 7 mium oxide) was impregnated r hours). Aconcentration Of platinum Of about platinum (catalyst 232). Thispromoted catalyst the chromlum tion (catalyst 232) gives much greaterconversions in short in lo ed for the c clization of normal hep- 6 n eun del the same co r iditions as shown in Ex- 0 cycle operatlonr isappmximately 25% efficient in 7 -hour cycles and is even definite] u ioam ollows. y 5 per r ample m The results obt ed were as I in 10-hourcycles. Over about 25 hours the aver- Average conv rsion t toluene ageconversions are about equal. Catalyst 176 over the first ten hours=1'l%65 containingabout 1.5% platinum -(based on the Bromine number=9 amountof chromium in the chromium oxide) when the hydrogen diluent wasreplaced by an gives much superior nv rsi ns in Short cycle equal amountof nitrogen, the results obtained Operation. 7 /2-hour cycle operationand 10-hour were as follows; cycle operation, and even the averageconversion obtained in 25-hour cycle operation are improved.

Aver e conversion to toluene Example V therefore clearly illustrates thee'flfect over the first t n h0111'$=31% of the concentration of promoterand the ad- Bromine numb r= vantageous results made possible by thepresent It is seen that, by comparing Examples III and method,especially when using short cycle opera- IV, the promotion of thecatalyst with as little 7: tion.

Example VI A conventional chromium oxide-alumina cycli- Temperature=490C., Pressure=1 atmosphere Liquid hourly space velocity=0.33

Conversions to toluene obtained initially, at the maximum and theaverage obtained over the first 7 V2, 10 and 25 hours of operation aregiven in the following table. The results obtained with a comparablecatalyst to which no palladium promoter was added are given forcomparison.

Non- Palladium- Conversion to toluene promoted promoted catalystcatalyst 25 hours average.

It is seen from these results that palladium is essentially as effectivea promoter for cyclizationdehydrogenation as platinum. The initialconversions obtained with palladium-promoted catalysts are slightlylower, but the averages in medium cycle operation are equal to, if notslightly better than, those obtained with platinumpromoted catalysts.Other elements of Group VIII are not equivalent to platinum and/orpalladium in their promoting eflect. Cobalt, for instance, when appliedto the above catalyst 57 (0.08%) under conditions comparable with thoseof Example VI afiords average conversions of only 41.7%, 39.8% and 30.4%for the first 7%,10 and 25 hours, respectively. Nickel and ruthenium actsimilarly. 7

Example VII Two comparable experiments were made using theabove-described catalyst 234 (containing 0.085% Pt) in which the normalheptane feed was altered by the addition 01' 0.05% and 0.25%,respectively. of sulfur in the form of diethyl sulfide. The deviationsof the conversion curves for both of the experiments from those obtainedwith pure normal heptane feed with the same catalyst were within thelimits of error of the measurements. The experiment with the heptanehaving the higher suliur content, in tact, gave slightly betterconversions than were obtained with the sulfur-tree teed.

The advantage of the present process over the prior art process such asdescribed above is that," due to the specific promoting effect of thespecified quantities of platinum and/or palladium on oyclizing metalcompound catalysts, greatly improved conversions may be obtained. As isillustrated in the above examples, the improved conversions areparticularly pronounced in the initial operating stages, i. 'e. duringthe first few hours of processing after each regeneration. The presentprocess is therefore especially advantageous in that it allows thecyclization to be ef- Iected with much higher conversions with shortcycle operation. The exceptional advantage of the present process inshort cycle operation will be more clearly evident from the followingconsideratipns:

- (1) In catalytic cyclization it is a general rule that catalysts whichshow the highest cyclization activity decline in activity taster thanthose having lower activities. This refers to the temporary loss ofactivity which is caused by the deposition on the catalyst of smallamounts of carbonaceous deposits and is probably due to the fact thatthe amount of carbonaceous deposits formed is more or less proportionalto the amount of reaction catalyzed. As a result, in the initial stagesof operation, i. e. in the first 2-10 hours after any regeneration, thesuperiority of the promoted catalyst over the non-promoted catalyst isgreater than after long periods or operation.

(2) Cyclization catalysts 'do not, in general, exhibit their maximumactivity immediately upon being put on-stream but require a certain'induction period (generally in the order of 1-8 hours), during whichlower than optimum conversions are obtained. The promoted catalysts usedin the process of the present invention, on the other hand, afiordmaximum conversions almost immediately upon being put on-stream, i. e.in the process 01 the present invention the induction period issubstantially absent. As a result of these two factors the initialconversions to aromatic hydrocarbons obtainable in the present processare often several times as high as those obtained by prior art methods,and conversions over short cycle periods are much superior. The averageconversions over long cycle periods, although superior to those usingprior art cyclization catalysts, are not superior in the outstandingdegree that they are in short cycle operation.

I claim as my invention:

1. Process for the production 01 aromatic nydrocarbons from aliphatichydrocarbons having from six to twelve carbon atoms which comprisescontacting the aliphatic hydrocarbon under cyclizing conditions with asolid compound catalyst consisting essentially of iromabout 2% --i'romsix to twelve carbon atoms which comprises contacting the aliphatichydrocarbon under cyclizing conditions with a solid compound catalystconsisting essentially of a cyclizing oxide of a metal selected from theleft-hand column of group VI of the periodic table supported upon amajor proportion of a stabilizing carrier consisting essentially ofalumina alpha monohydrate and promoted with about 0.2% to 2% (based onthe amount of metal in the cyclizing compound) of a metal selected fromthe group consisting of platinum and palladium.

3. Process for the production-,0! aromatic hydrocarbons from aliphatichydrocarbons having from six to twelve carbon atoms which comprisescontacting the aliphatic hydrocarbon under cyclizing conditions with asolid compound catalyst consisting essentially of a cyclizing oxide of ametal selected from the left-hand column of group VI of the periodictable supported upon a major proportion of an adsorptive alumina andpromoted with about 0.2% to 2% (based on the amount of metal in thecyclizing compound) of U from six to twelve-carbon atoms which comprisesWlth from about 0.2% to 2% aamosa contacting the aliphatic hydrocarbonunder cyclizing conditions with a solid compound catalyst consistingessentially of from about 2% to 30% chromium as chromium oxide supportedupon a stabilizing carrier or relatively low catalytic activity andpromoted withabout .07% to .2% of platinum.

5. Process for the production of aromatic hydrocarbons from aliphatichydrocarbons having from six to twelve carbon atoms which comprisescontacting the aliphatic hydrocarbon under cyclizing conditions with asolid compound catalyst consisting essentially of a cyclizing compoundof chromium supported upon a major proportion of a stabilizing carrierof relatively low catalytic activity and promoted with from about 0.2%td2% (based' on the amount of metal in the cyclizing compound) of.platinum.

6. Process for the production of aromatic hydrocarbons from aliphatichydrocarbons having from six to twelve carbon atoms which comprisescontacting the aliphatic hydrocarbon under cyclizing conditions with asolid compound catalyst consisting essentially of a cyclizing compoundoi a metal selected from the left-hand column of group VI of theperiodic table supported upon a major proportion of a stabilizingcarrier of relatively low catalytic activity and promoted (based on theamount of metal in the cyclizing compound) of platinum.

7. Process for the production of aromatic hydrocarbons from aliphatichydrocarbons having from six to'twelve carbon atoms which comprisescontacting the aliphatic hydrocarbon under cyclizing conditions with asolid compound catalyst consisting essentially of chromium oxidesupported upon a major proportion of a stabilizing carrier of relativelylow catalytic activity and promoted with about 0.2% to 2% (based on theamount of metal in the cyclizing compound) of a metal selected fromthegroup consisting of platinum and palladium.

8. Process for the production of aromatic hydrocarbons from aliphatichydrocarbons having from six to twelve carbon atoms which comprisescontacting the aliphatic hydrocarbon under cyclizing conditions with asolid compound catalyst consisting essentially of a cyclizing oxide of ametal selected from the left-hand column of group VI of the periodictable supported upon a major proportion of a stabilizing carrier ofrelatively low catalytic activity and promoted with about 0.2%.to 2%(based on the amount of metal in the cyclizing compound) of a metalselected from the group consisting of platinum and palladium.

9. Process for the production of aromatic hydrocarbons from aliphatichydrocarbons having from six to twelve carbon atoms which comprisescontacting the aliphatic hydrocarbon under cyclizing conditions with asolid compound catalyst consisting essentially of a cyclizing oxide of ametal selected from the left-hand columns of groups IV, V and VI of theperiodic table supported upon a major proportion of a stabilizingcarrier of relatively low catalytic activity and promoted with about0.2% to 2% '(based on the amount of metal in the cyclizing compound) ofa metal selected from the group consisting of platinum and palladium.

10. Process for the production of aromatic hydrocarbons from aliphatichydrocarbons having from six to twelve carbon atoms which comdercyclizing conditions with a solid compound catalyst consistingessentially of a cyclizing compound of chromium supported upon amajorproportion of a stabilizing carrier, of relatively low catalyticactivity and promoted withabout to 2% (based on the amount 01 metal inthe cyclizing compound) oi a metal selected from the group consisting ofplatinum and palladium.

11. Process for the production of aromatic hydrocarbons from aliphatichydrocarbons having from six to twelvecarbon atoms which comprisescontacting the aliphatic hydrocarbon under cyclizing conditions with asolid compound catalyst consisting essentially of a cyclizing compoundof a metal selected from the left-hand column of group VI of theperiodic table supported upon a major proportion of a stabilizingcarrier of relatively low catalytic activity and promoted with about0.2% to 2% (based on the amount 01 metal in the cyclizing compound) of ametal selected from the group consisting of platinum and palladium.

12. Process for the production of aromatic hydrocarbons from aliphatichydrocarbons having from six to twelve carbon atoms which comprisescontacting the aliphatic hydrocarbon under cyclizing conditions with asolid compound catalyst consisting essentially of a cyclizing compoundof a metal selected from the left-hand columns of groups IV, V and VI ofthe periodic table supported upon a major proporion of a stabilizingcarrier of relatively low catalytic activity and promoted with about0.2% to 2% (based on the amount of metal in the cyclizing compound) of ametal selected from the group consisting of platinum and palladium.

13. Process for the production of aromatic hydrocarbons from aliphatichydrocarbons having from 6 to 12 carbon atoms which comprises contactingthe aliphatic hydrocarbon under cyclizing conditions with a solidcompound catalyst con sisting essentially of a cyclizing compound of ametal selected from the left-hand columns of groups IV, V and VI of theperiodic table supported upon a major proportion of a stabilizingcarrier consisting essentially of alumina alpha monohydrate and promotedwith about 0.2% to prises contacting the aliphatic hydrocarbon un- 76 2%based on the amount of metal in the cyclizing compound) of a metalselected from the group consisting of platinum and palladium.

14.. Process for the production of aromatic hydrocarbons from aliphatichydrocarbons having from 6 to 12 carbon atoms which comprises contactingthe aliphatic hydrocarbon under cyclizing conditions with a solidcompound catalyst consisting essentially of a cyclizing oxide of a metalselected from the left-hand columns of groups IV, V and VI of theperiodic table supported upon a major-proportion of a stabilizingcarrier consisting essentially of alumina alpha monohydrate and promotedwith about 0.2% to 2% (based on the amount of metal in the cyclizingcompound) of a metal selected from the group consisting of platinum andpalladium.

15. Process for the production of aromatic hydrocarbons from aliphatichydrocarbons having from 6 to 12 carbon atoms which comprises contactingthe aliphatic hydrocarbon under cyclizing conditions with a solidcompound catalyst,

consisting essentially of a cyclizing compo d of chromium supported upona major prop ion of a stabilizing carrier consisting essenti of aluminaalpha monohydrate and promoted with about 0.2% to 2% (based on theamount ofmetal in the cyclizing compound) or a metal selected from thegroup consistingof platinum and cameos consisting essentially ofchromium oxide supported upon a major proportion of a stabilizingcarrier consisting essentially of alumina alpha monohydrate and promotedwith about 0.2% to 2% (based on the amount of chromium) 01' a 'metalselected from the group consisting of platinum and palladium.

- BERNARD S. GREENSFELDER.

